1. Field of the Invention
The present invention relates to an optical disc apparatus for, from an optical disc on which a digital signal including time data is recorded, demodulating and outputting the digital data, and more particularly to an optical disc apparatus which enables a display device to OSD-display time data while displaying image data.
2. Description of the Related Art
On some of optical discs that are currently used, time data is recorded together with image data. An apparatus (optical disc apparatus) for reproducing such an optical disc reads out digital data recorded on the optical disc while separately reading out image data and time data, and then demodulates the data. The demodulated image data is converted so as to meet the specification such as aspect ratio of a display device on which the image data is to be displayed. Thereafter, the image data and the time data are formed into a composite image of a predetermined format while being synchronized with each other, and the composite image is supplied to the display device. The display device displays an image in which a time based on the time data is OSD-displayed.
In such an optical disc apparatus, it is important to correctly read out information recorded on an optical disc. JP-A-63-20726 discloses a method in which, when an error signal value that is sampled at a certain timing is inadequate, an error signal value that is sampled immediately before the timing is used in place of the error signal value at the certain timing. In this way, the sampling control is always performed to correctly read and write information.
In such an optical disc apparatus, when time data is correctly readout, the true time, the time based on the read-out time data (hereinafter, referred to as “read-out time”), and the time based on the output (displayed) time data (hereinafter, referred to as “display time”) always coincide with one another. When the recording face of an optical disc is damaged, for example, there often arises a case where time data cannot be correctly read out. In such a case, time data that is different from the true time is output. Even when the present read-out time lags the previous display time, for example, the present read-out time is set as the display time and output as a new display time, thereby causing the time in the display to reversely progress.
Thus, a conventional optical disc apparatus employs a flow shown in FIG. 4 in a range from extraction of time data to output of the time data. This flow is repeatedly executed during the reproduction.
FIG. 4 shows the flow in the range from extraction of time data to output of the time data.
As shown in FIG. 4, when time data in digital data is read out, the read-out time data (read-out time) is compared with the time data (display time) that is output immediately before the reading (s101→s102). If the read-out time leads the immediately previous display time, the display time is updated to the present read-out time and then output (s103→s104→s106). The display time updated in s104 is fed back to be used as the reference for the subsequent comparison with the read-out time. By contrast, if the read-out time lags the immediately previous display time, the display time is not updated, and the immediately previous display time is maintained to be output (s103→s105→s106).
However, in a conventional optical disc apparatus, when the read-out time that is presently read out leads the display time that is previously output for display, the display time is updated, and the updated display time is output. When the read-out time largely leads the display time, largely led display time is output. When the read-out time leads the previous display time by 1 hour, for example, the display time is updated, and the time which leads the previous display time by 1 hour is output. Even when a read-out time coincident with the true time is thereafter obtained (for example, time data indicating the true time after an elapse of 2 seconds is obtained), the read-out time lags the display time, and the display time is not updated because the display time which largely leads (1 hour in the above case) is output immediately before the reading and the display time is used as the reference. In other words, the display time does not coincide with the true time until the largely led time elapses, and the same time continues to be displayed.
When a time that is largely different from the true time is displayed and the time does not progress for a long time period, the user feels uncomfortable and the time display is meaningless.